1. Field of the Invention
The invention relates to an apparatus and method for inspecting small articles, such as in particular tablets, film tablets, dragees, capsules, etc., the articles being held for inspection purposes by means of vacuum on supports rotating about axes.
2. Description of the Prior Art
Tablets, etc. must to an increasing extent be inspected for defects. If a precisely defined tablet treatment dose is predetermined, this dose would be modified if a patient should ingest a tablet with a break. In the case of film tablets and dragees, the active ingredients contained therein must be supplied in delayed form to the body and for this purpose the tablets and dragees are provided with a coating. If the coating is damaged or at least in part absent, then there is a change to the characteristics and/or action of the ingested medicament. This must be avoided and can be prevented if the tablets, film tablets, dragees, capsules, etc. are inspected for lack of damage and completeness. It is necessary to check their entire surface. This can take place by means of an apparatus for inspecting such articles.
In addition, it must be ensured in the case of such an apparatus that during the inspection of the articles such as tablets and the like no residues of the tested articles are left behind on the conveying members, even in very small amounts, e.g. in the form of dust. Thus, if the same conveying members were then used for other products such as tablets, etc., the residues left behind by the previously inspected products, such as e.g. in dust form, could adhere to the subsequently inspected products, which must be completely avoided. To prevent this all the product-contacted parts of the apparatus must be cleaned. However, this takes a considerable time and can lead to undesired stoppage times on the part of the inspection apparatus.
German patent 42 02 172 discloses an apparatus of the aforementioned type, in which the articles to be tested are supplied to receptacles of at least one first, rotary disk. They can optionally be held with suction force in the receptacles. There is no precise supply to the receptacles. Following the inspection of the top of the articles they are transferred to a second disk located above and running synchronously to the first, rotary disk, where the articles hang on suction holes, so that their underside can be inspected. As a function of the inspection result the articles are removed from the second disk and sorted. The delivery from the first to the second disk takes place by raising the articles on the first disk until they are in the immediate holding range of the second disk. As a result, for at least a short time, the articles are subject to an influence disturbing the positioning through centrifugal force. Thus, either the speeds of the disks must be reduced, so that there is an output limitation, or no precise positioning is possible. An imprecise positioning can lead both on the first and second disks to articles such as e.g. spherical tablets assuming an inclined position relative to the detection direction, which leads to optically distorted images. Moreover, when using video cameras the image detail must be enlarged, which requires a higher calculating power for evaluation and therefore leads to an output limitation and/or a poorer resolution and correspondingly inferior inspection results. The inclined positions are also problematical with respect to a reflection-free illumination. Because the centrifugal forces act at right angles to the holding forces, the effective holding force only corresponds to the frictional force, which is produced by the holding force. This also leads to a significant speed reduction. The undefined supply of the articles to the first disk is also disadvantageous. As a result of the undefined residence time and very high relative speeds between the articles and the first disk, the articles to be tested can even be damaged. The use of movable mechanical components, such as e.g. a ram leads to considerable problems when cleaning the apparatus. The application of a vacuum by the suction channels, e.g. in the transfer area from the first to the second disk, requires the most careful cleaning of the ram and the suction channels, in order to avoid cross-contaminations.
According to German patent 36 08 398 articles are conveyed by a conveying mechanism, which essentially comprises two driven, endless belts, which are guided over pulleys with an adjustable reciprocal spacing and are received in stationary plates. The articles are subject to suction action via the spacing or gap and are in this way held on the belts. Such a first conveying mechanism on which the articles are located is followed by a second mechanism on which they are suspended. The articles are visually observed by means of several line cameras. For observing the lateral faces the two conveyor belts of a conveying mechanism have a relative speed with respect to one another. In this way the articles are then rotated about their vertical axis. According to this document, the articles are separated on a rotary table with guiding devices and sorting gates.
In the case of line cameras the resolution and therefore the detection precision is dependent on the conveying speed of the articles to be inspected. Apart from possible operating errors this also suffers from the disadvantage that the throughput is inversely proportional to the dimensions of the articles to be inspected, i.e. the throughput decreases with increasing length of the articles in the conveying direction. As a result of the in part concealed gaps in the conveying system, the cleaning of the apparatus is also extremely time-consuming. As a result of the rotation of the articles by the conveying mechanism it is only possible to a limited extent to observe their lateral faces. The rotation of the articles by the relative movement of the conveyor belts even in the case of substantially round articles such as tablets can lead to inclined positions and therefore to distortions and/or light reflections and is not even possible with oblong tablets. The sought after complete surface check is then not possible or is only possible with limitations. The nature of the separation in the case of this apparatus also involves high cleaning costs and a high damage risk for the articles.